Now showing items 261-280 of 316

    • Wei-type duality theorems for matroids 

      Britz, Thomas; Johnsen, Trygve; Mayhew, Dillon; Shiromoto, Keisuke (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      We present several fundamental duality theorems for matroids and more general combinatorial structures. As a special case, these results show that the maximal cardinalities of fixed-ranked sets of a matroid determine the corresponding maximal cardinalities of the dual matroid. Our main results are applied to perfect matroid designs, graphs, transversals, and linear codes over division rings, in each ...
    • Bayesian multiscale analysis of images modeled as Gaussian Markov random fields 

      Thon, Kevin Otto; Rue, Håvard; Skrøvseth, Stein Olav; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      A Bayesian multiscale technique for the detection of statistically significant features in noisy images is proposed. The prior is defined as a stationary intrinsic Gaussian Markov random field on a toroidal graph, which enables efficient computation of the relevant posterior marginals. Hence the method is applicable to large images produced by modern digital cameras. The technique is demonstrated ...
    • Multicentennial Variability of the Sea Surface Temperature Gradient across the Subpolar North Atlantic over the Last 2.8 kyr 

      Miettinen, A.; Divine, D.V.; Koc, N.; Godtliebsen, F.; Hall, I.R. (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assemblages is generated from a marine sediment core from the northern subpolar North Atlantic. The record is compared with the aSST record from the Norwegian Sea to explore the variability of the aSST gradient between these areas during the late Holocene. The aSST records demonstrate the opposite climate tendencies ...
    • Automatic nematode detection in cod fillets (Gadus morhua L.) by hyperspectral imaging 

      Sivertsen, Agnar Holten; Heia, Karsten; Hindberg, Kristian; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      Detection of objects embedded in tissue, using visible light, is difficult due to light scattering. The optical properties of the surrounding tissue will influence the spectral characteristics of the light interacting with the object, and the spectral signature observed from the object will be directly affected. A method for calibrating the spectral signature of small objects, embedded in translucent ...
    • Pairwise scale space comparison of time series with application to climate research 

      Godtliebsen, Fred; Holmström, L.; Miettinen, A.; Erästö, P.; Divine, Dmitry V; Koc, Nalan (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      In this paper, we study how sea surface temperature variations in the North Atlantic and the Norwegian Sea are correlated with the climate in the Northern Hemisphere in late Holocene. The analysis is performed by testing statistical hypotheses through novel scale space methodologies. In late Holocene, the proposed techniques reveal that the climate development in the subpolar North Atlantic has been ...
    • Automatic Segmentation of Dermoscopic Images by Iterative Classification 

      Zortea, Maciel; Skrøvseth, Stein Olav; Schopf, Thomas Roger Griesbeck; Kirchesch, Herbert M.; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      Accurate detection of the borders of skin lesions is a vital first step for computer aided diagnostic systems. This paper presents a novel automatic approach to segmentation of skin lesions that is particularly suitable for analysis of dermoscopic images. Assumptions about the image acquisition, in particular, the approximate location and color, are used to derive an automatic rule to select small ...
    • Thousand years of winter surface air temperature variations in Svalbard and northern Norway reconstructed from ice-core data 

      Divine, Dmitry V; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      Two isotopic ice core records from western Svalbard are calibrated to reconstruct more than 1000 years of past winter surface air temperature variations in Longyearbyen, Svalbard, and Vardø, northern Norway. Analysis of the derived reconstructions suggests that the climate evolution of the last millennium in these study areas comprises three major sub-periods. The cooling stage in Svalbard (ca. ...
    • Scale Space Methods for Analysis of Type 2 Diabetes Patients' Blood Glucose Values 

      Skrøvseth, Stein Olav; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      We describe how scale space methods can be used for quantitative analysis of blood glucose concentrations from type 2 diabetes patients. Blood glucose values were recorded voluntarily by the patients over one full year as part of a self-management process, where the timeand frequency of the recordings are decided by the patients. This makes a unique datasetin its extent, though with a large variation ...
    • Matematisk kulturhistorie : artikkelsamling 

      Thorvaldsen, Steinar (Book; Bok, 2002-08)
    • A stochastic theory for temporal fluctuations in self-organized critical systems 

      Rypdal, Martin; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
    • Finite Larmor radius influence on MHD solitary waves 

      Mjølhus, Einar (Journal article; Tidsskriftartikkel; Peer reviewed, 2009)
    • Vanishing of the entropy pseudonorm for certain integrable systems 

      Kruglikov, Boris Serafimovich; Matveev, VS (Journal article; Tidsskriftartikkel; Peer reviewed, 2006)
    • A propagation-separation approach to estimate the autocorrelation in a time-series 

      Divine, Dmitry V; Polzehl, J; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
    • Bayesian modeling and significant features exploration in wavelet power spectra 

      Divine, Dmitry V; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)
    • DeltaProt : a software toolbox for comparative genomics 

      Thorvaldsen, Steinar; Flå, Tor; Willassen, Nils P (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)
    • Nijenhuis tensors in pseudoholomorphic curves neighborhoods 

      Kruglikov, Boris (Working paper; Arbeidsnotat, 2000)
      In this paper we consider the normal forms of almost complex structures in a neighborhood of pseudoholomorphic curve. We define normal bundles of such curves and study the properties of linear bundle almost complex structures. We describe 1-jet of the almost complex structure along a curve in terms of its Nijenhuis tensor. For pseudoholomorphic tori we investigate the problem of pseudoholomorphic ...
    • Symmetry approaches for reductions of PDEs, differential constraints and Lagrange-Charpit method 

      Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-12-20)
      Many methods for reducing and simplifying differential equations are known. They provide various generalizations of the original symmetry approach of Sophus Lie. Plenty of relations between them have been noticed and in this note a unifying approach will be discussed. It is rather close to the differential constraint method, but we make this rigorous basing on recent advances in compatibility ...
    • Strictly non-proportional geodesically equivalent metrics have htop(g) = 0 

      Matveev, Vladimir S.; Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2004-10-24)
      If a closed manifold M possesses two Riemannian metrics which have the same unparameterized geodesics and are not strictly proportional at each point, then the topological entropy of both geodesic flows is zero. This is the main result of the paper and it has many dynamical and topological corollaries. In particular, such a manifoldM should be finitely covered by the product of a rationally ...
    • Invariants and submanifolds in almost complex geometry 

      Kruglikov, Boris (Chapter; Bokkapittel, 2007-12-20)
      In this paper we describe the algebra of differential invariants for GL(n,C)-structures. This leads to classification of almost complex structures of general positions. The invariants are applied to the existence problem of higher-dimensional pseudoholomorphic submanifolds.
    • The Kobayashi pseudodistance on almost complex manifolds 

      Overholt, Marius; Kruglikov, Boris S. (Working paper; Arbeidsnotat, 1997-03-06)
      We extend the definition of the Kobayashi pseudodistance to almost complex manifolds and show that its familiar properties are for the most part preserved. We also study the automorphism group of an almost complex manifold and finish with some examples.